1. Field of Invention
The present invention is directed to materials and methods for forming ceramic assemblies with adhesive materials having desirable magnetic, abrasive, and thermal properties.
2. Discussion of Related Art
Circulators and isolators are passive electric devices that are used in radio frequency (RF) systems, for example, microwave systems, to permit a signal to pass in one direction while providing high isolation to reflected energy in the reverse direction. Low intermodulation isolators may be used for cellular base station combiners and amplifiers. Circulators and isolators commonly include an assembly comprising a disc-shaped ferrite or other ferromagnetic ceramic element, disposed concentrically within a dielectric annulus. The dielectric annulus is similarly commonly made of ceramic material.
One method of production of such magnetic-dielectric assemblies is to use an organic adhesive to glue a ceramic ferrite rod into a ceramic dielectric tube, followed by cutting using an annular saw. The cut segments are cut oversize then ground to final thickness and flatness. Assemblies using organic adhesives often heat up during machining, causing the adhesive to swell at the cut surface, producing a surface bump and reducing overall surface smoothness, which may affect the performance of devices such as isolators. In addition, softened adhesive may in some cases adhere to portions of the cutting blade, causing it to flex or bend, also reducing the smoothness and/or increasing the variation in thickness of the cut magnetic-dielectric assemblies. Many organic adhesives have a significant high frequency magnetic and/or electric loss tangent.
Another method which may facilitate direct cutting to size of magnetic-dielectric disc assemblies is the use of co-fired assemblies which do not utilize an adhesive. However, co-fired assemblies are not possible for all combinations of dielectric and magnetic materials because of differences in thermal expansion between the two materials.